Malic Acid is the primary acid found in fruits such as apples, cherries, peaches and plums.
It is typically used in wines that are naturally lacking in acid. Wines too low in acid are flat tasting can also be susceptible to spoilage. Malic Acid adds a liveliness to the wine and helps to bring out it`s fruity flavors. If there is too much Malic acid in the wine it can taste 'sour'.
Having the proper level of acidity will help to establish a vigorous fermentation.